The present invention relates to new catalyst compositions and to methods for the polymerization of alpha-olefins using these improved catalysts.
Ionic coordination polymerization catalysts which are the interaction products of: (1) a compound of a metal of Group IV-B or V-B of the periodic table of elements; and, (2) an organometallic compound of a metal of Group III-A of the periodic table are well known. Such catalysts are disadvantageous in that low catalyst activity (weight of polymer per weight of transition metal compound per unit time) is obtained in many cases; in that the polymerization rate is undesirably slow unless relatively high concentrations of catalyst are used; and in that when a soluble catalyst system is used, the activity often decreases rapidly during the course of polymerization.
The present invention is based on the surprising discovery that a catalyst based on a vanadium compound and an organometallic compound (hereinafter also referred to as the primary catalyst system) is made more effective and/or maintains its activity for a longer period and/or can be reactivated after it begins to lose activity, if an activator is added to said catalyst. In some cases the addition of the activator also serves to regulate the molecular weight. A catalyst activator is a material or compound which reacts with a spent catalyst, returning the catalyst to a condition in which it can continue to promote the intended chemical reaction. Earlier combinations of similar catalysts and their activators are described in U.S. Pat. Nos. 3,377,325 using sulfur activation, U.S. Pat. No. 3,377,326 using phosphorous trichloride and 2-nitropropane activation, U.S. Pat. No. 3,441,546 using organic nitro compound activation, U.S. Pat. No. 3,444,149 using nitroso compound or quinone activation, U.S. Pat. No. 3,462,399 with activation by organic nitrates, organic nitrites, azoxy compounds, special organo metallic compounds or alkyl disulfide and U.S. Pat. No. 3,507,843 using phosphorous trichloride activation.